I suspect this topic has come up for discussion before, and I've always thought of Colonel Mortimer as Lee Van Cleef's signature role, not to mention his best performance. But what if Van Cleef hadn't been available in 1965? Who would have beenan adequate substitute? Apparently Lee Marvin and Robert Ryan were both approached by Leone. Ryan in particular, I think, would have been good casting as an honourable man of an older generation. (Not that Marvin wouldn't have been great too, in his own way.) Also quite like the idea of either Joel McCrea or Randolph Scott - although it's hard to imagine the latter, who had by then retired, comfortably wealthy, taking a trip to Spain to make a few bucks. But just imagine Randolph Scott facing off against the likes of Kinski and Volonte... (Given the maturity of these actors, it would probably make more sense for Mortimer to be avenging his daughter rather than his sister).

Stewart would certainly have been interesting, though he would've bust the budget. And Fonda, obviously - yet that might somehow 'clash' with his turn as Frank in OUATITW. (Just as, in a way, I'd rather remember Van Cleef as Mortimer and see someone else - Jack Palance, maybe - in GBU.)

Apparently Charles Bronson was also approached - but he would surely have seemed miscast as a Colonel from the Carolinas? As would Yul Brynner.)

Gregory Peck or William Holden - might have been interesting, but both too expensive. Dana Andrews, possibly?

Maybe a desperate Leone would even have considered Stewart Granger? Or his old pal from The Colossus of Rhodes, Rory Calhoun?

But Marvin wasn't simply approached. He had actually signed for the movie, according to Leone, only to retire at the start of the weekend before shooting began because he veered toward Cat Ballou, forcing Leone to fly on the Saturday to the USA to find the man (whose name he didn't remember but found in the actors directory book) he remembered from High Noon and How the West Was Won and who presented himself at his hotel on the Sunday. I'm quoting from the Gabutti's book which I'm currently reading.